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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jiri Olsa <jolsa@redhat.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>
Subject: Re: [RFC PATCH bpf-next 1/4] bpf: Allow trampoline re-attach
Date: Mon, 05 Apr 2021 16:15:54 +0200	[thread overview]
Message-ID: <87ft04rf51.fsf@toke.dk> (raw)
In-Reply-To: <YGsZ0VGMk/hBfr2y@krava>

Jiri Olsa <jolsa@redhat.com> writes:

> On Sat, Apr 03, 2021 at 11:21:55AM -0700, Alexei Starovoitov wrote:
>> On Sat, Apr 03, 2021 at 01:24:12PM +0200, Toke Høiland-Jørgensen wrote:
>> > >  	if (!prog->aux->dst_trampoline && !tgt_prog) {
>> > > -		err = -ENOENT;
>> > > -		goto out_unlock;
>> > > +		/*
>> > > +		 * Allow re-attach for tracing programs, if it's currently
>> > > +		 * linked, bpf_trampoline_link_prog will fail.
>> > > +		 */
>> > > +		if (prog->type != BPF_PROG_TYPE_TRACING) {
>> > > +			err = -ENOENT;
>> > > +			goto out_unlock;
>> > > +		}
>> > > +		if (!prog->aux->attach_btf) {
>> > > +			err = -EINVAL;
>> > > +			goto out_unlock;
>> > > +		}
>> > 
>> > I'm wondering about the two different return codes here. Under what
>> > circumstances will aux->attach_btf be NULL, and why is that not an
>> > ENOENT error? :)
>> 
>> The feature makes sense to me as well.
>> I don't quite see how it would get here with attach_btf == NULL.
>> Maybe WARN_ON then?
>
> right, that should be always there
>
>> Also if we're allowing re-attach this way why exclude PROG_EXT and LSM?
>> 
>
> I was enabling just what I needed for the test, which is so far
> the only use case.. I'll see if I can enable that for all of them

How would that work? For PROG_EXT we clear the destination on the first
attach (to avoid keeping a ref on it), so re-attach can only be done
with an explicit target (which already works just fine)...

-Toke


  reply	other threads:[~2021-04-05 14:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-28 11:26 [RFC PATCH bpf-next 0/4] bpf: Tracing programs re-attach Jiri Olsa
2021-03-28 11:26 ` [RFC PATCH bpf-next 1/4] bpf: Allow trampoline re-attach Jiri Olsa
2021-03-30  1:18   ` Song Liu
2021-04-03 11:24   ` Toke Høiland-Jørgensen
2021-04-03 18:21     ` Alexei Starovoitov
2021-04-05 14:08       ` Jiri Olsa
2021-04-05 14:15         ` Toke Høiland-Jørgensen [this message]
2021-04-05 21:58           ` Jiri Olsa
2021-04-05 14:06     ` Jiri Olsa
2021-03-28 11:26 ` [RFC PATCH bpf-next 2/4] selftests/bpf: Add re-attach test to fentry_test Jiri Olsa
2021-03-30  1:23   ` Song Liu
2021-03-30 20:02     ` Jiri Olsa
2021-03-28 11:26 ` [RFC PATCH bpf-next 3/4] selftests/bpf: Add re-attach test to fexit_test Jiri Olsa
2021-03-28 11:26 ` [RFC PATCH bpf-next 4/4] selftests/bpf: Test that module can't be unloaded with attached trampoline Jiri Olsa
2021-03-30  6:12   ` Song Liu

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